Pulps — Kraft liquor — Determination of hydrosulphide ion concentration using potentiometric titration

This document describes a procedure for the determination of sulphide, i.e. the hydrosulphide ion concentration, in white, oxidized white and green liquors, as well as in black liquor having a dry matter content up to 40 %. The determination also includes the sulphide part of any polysulphide present in the solution.

Pâtes — Liqueur Kraft — Détermination de la concentration en ions hydrosulfurés par titrage potentiométrique

General Information

Status
Published
Publication Date
09-Mar-2023
Current Stage
6060 - International Standard published
Start Date
10-Mar-2023
Due Date
20-Dec-2023
Completion Date
10-Mar-2023
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INTERNATIONAL ISO
STANDARD 23777
First edition
2023-03
Pulps — Kraft liquor — Determination
of hydrosulphide ion concentration
using potentiometric titration
Pâtes — Liqueur Kraft — Détermination de la concentration en ions
hydrosulfurés par titrage potentiométrique
Reference number
ISO 23777:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 23777:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 23777:2023(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Reagents ........................................................................................................................................................................................................................ 2

6 Apparatus .................................................................................................................................................................................................................... 3

7 Sampling and sample pretreatment................................................................................................................................................3

7.1 General ........................................................................................................................................................................................................... 3

7.2 White, green and black liquors ................................................................................................................................................ 3

7.3 Oxidized white liquors..................................................................................................................................................................... 3

8 Procedure ....................................................................................................................................................................................................................4

8.1 General ........................................................................................................................................................................................................... 4

8.2 White, green and black liquors ................................................................................................................................................ 4

8.3 Oxidized white liquors..................................................................................................................................................................... 4

8.4 Titration........................................................................................................................................................................................................ 4

9 Calculation .................................................................................................................................................................................................................. 5

10 Report .............................................................................................................................................................................................................................. 6

Annex A (informative) Precision data ................................................................................................................................................................ 7

Bibliography ................................................................................................................................................................................................................................ 8

iii
© ISO 2023 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 23777:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2023 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 23777:2023(E)
Pulps — Kraft liquor — Determination of hydrosulphide
ion concentration using potentiometric titration
1 Scope

This document describes a procedure for the determination of sulphide, i.e. the hydrosulphide ion

concentration, in white, oxidized white and green liquors, as well as in black liquor having a dry matter

content up to 40 %. The determination also includes the sulphide part of any polysulphide present in

the solution.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
hydrosulphide ion concentration
concentration in white, black and green liquors or oxidized white liquor

Note 1 to entry: Practically no S ions are present in white, oxidized white, green, and black liquors because of

hydrolysis according to the reaction:
2−− −
SH+→OHSO+ H
4 Principle

The procedure is based on potentiometric titration with silver nitrate solution according to

reaction (1) and (2):
−− +
HS ++OH 2Ag →+Ag SH O (1)
22()black ppt
CH SA+→gAgCHS (2)
33 ()yellow ppt

Sulphite ions are added to the sample solution in order to dissolve any polysulphide ions that are

present according to reaction (3):
2−−2−−2 −
nSOS++SH On→+SO HS +OH (3)
3 n 22 3

Each polysulphide ion thus contributes one sulphide ion to the sulphide content. As the titration is

performed in alkaline solution, thiosulphate or sulphite ions do not interfere in the determination.

© ISO 2023 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 23777:2023(E)

When sulphite ions are added to organic polysulphides, mercaptide ions are produced according to

reaction (4):
2−− −
CH SSCHS+→OCH SSO +CH S (4)
33 3 33 3

For white, green and black liquor, this document is applicable for hydrosulphide ion concentrations

from 0,02 mol/litre to 2 mol/litre, provided that the volume of the original sample taken to analysis

is selected accordingly. For oxidized white liquors the standard is applicable to hydrosulphide ion

concentrations from 0,5 mmol/litre to 50 mmol/litre, provided that the volume of the original sample

taken to analysis is selected accordingly.
Precision data are available in Annex A.
5 Reagents
All chemicals shall be of analytical grade.
5.1 Water, use oxygen-free water for the preparation of the solutions.

NOTE Oxygen-free water can be prepared from distilled water either by boiling the water for 15 min or by

displacing the oxygen with nitrogen gas.

5.2 Silver nitrate 0,1 M, dissolve 17,0 g of dry silver nitrate, AgNO , in a 1 000 ml volumetric flask.

Stir and fill up to the mark with water (5.1). Determine the concentration in the following way:

Weigh approximately 750 mg of dried potassium chloride, KCl, to an accuracy of 0,5 mg into a 100 ml

volumetric flask and fill up to the mark with water (5.1). With a precision pipette, take 5 ml for titration

in distilled water. Titrate with the silver nitrate solution to the first inflection point. From the silver

nitrate consumption, a ml, calculate the silver nitrate concentration in moles/litre to four decimal

places.

Calculate the silver nitrate concentration, [AgNO ], in mol/litre, according to Formula (5):

5*b
AgNO = (5)
74,*5513 a*100
where
a is the silver nitrate consumption, in millilitres;
b is the amount of potassium chloride weighed, in milligrams;
74,551 3 is the relative molecular mass of KCl.

Store the silver nitrate solution in a dark glass bottle. Commercially available solutions of silver nitrate

may be used.

5.3 Sodium hydroxide solution 1 M, dissolve 40,0 g of NaOH in 1,0 litre of oxygen-free water (5.1).

5.4 Alkaline sodium sulphite solution approximately 0,5 M, dissolve 60,
...

2022-10-1711-25
ISO/FDIS 23777:2022(E)
Secretariat: SCC
ISO TC 6/WG 17
Pulps — Kraft liquor — Determination of hydrosulphide ion concentration using
potentiometric titration
---------------------- Page: 1 ----------------------
ISO/FDIS 23777:2022
2 © ISO #### – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 23777:2022(E)
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no

part of this publication may be reproduced or utilized otherwise in any form or by any means,

electronic or mechanical, including photocopying, or posting on the internet or an intranet, without

prior written permission. Permission can be requested from either ISO at the address below or

ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
Formatted: Font: 11 pt
Formatted: Space After: 6 pt, Line spacing: Exactly 11
© ISO 2022 – All rights reserved 3
© ISO 2022 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 23777:2022(E)
Contents

Foreword ........................................................................................................................................................... iv

1 Scope ....................................................................................................................................................... 1

2 Normative references ........................................................................................................................ 1

3 Terms and definitions ....................................................................................................................... 1

4 Principle ................................................................................................................................................ 2

5 Reagents ................................................................................................................................................ 2

5.1 General ................................................................................................................................................... 2

5.2 Silver nitrate 0,1 M ............................................................................................................................. 2

5.3 Sodium hydroxide solution 1 M ..................................................................................................... 3

5.4 Alkaline sodium sulphite solution approximately 0,5 M ......................................................... 3

5.5 Ammonia ............................................................................................................................................... 3

6 Apparatus .............................................................................................................................................. 3

6.1 General ................................................................................................................................................... 3

6.2 Automatic titration equipment ...................................................................................................... 3

6.3 Indicator electrode ............................................................................................................................. 3

6.4 Reference electrode ........................................................................................................................... 3

6.5 Pipette .................................................................................................................................................... 3

7 Sampling and sample pretreatment ............................................................................................. 4

7.1 General ................................................................................................................................................... 4

7.2 White, green and black liquors ...................................................................................................... 4

7.3 Oxidized white liquors ...................................................................................................................... 4

8 Procedure .............................................................................................................................................. 4

8.1 White, green and black liquors ...................................................................................................... 4

8.2 Oxidized white liquors ...................................................................................................................... 5

8.3 Titration................................................................................................................................................. 5

9 Calculation ............................................................................................................................................ 6

10 Report ..................................................................................................................................................... 7

Annex A (informative) Precision data ....................................................................................................... 8

Bibliography ....................................................................................................................................................... 9

Foreword ........................................................................................................................................................... iv

1 Scope ....................................................................................................................................................... 1

2 Normative references ........................................................................................................................ 1

3 Terms and definitions ....................................................................................................................... 1

4 Principle ................................................................................................................................................ 2

5 Reagents ................................................................................................................................................ 2

5.1 General ................................................................................................................................................... 2

5.2 Silver nitrate 0,1 M ............................................................................................................................. 2

Formatted: Font: 11 pt

5.3 Sodium hydroxide solution 1 M ..................................................................................................... 3

Formatted: Space After: 6 pt, Line spacing: Exactly 11

5.4 Alkaline sodium sulphite solution approximately 0,5 M ......................................................... 3

4 © ISO 2022 – All rights reserved
iv © ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 23777:2022(E)

5.5 Ammonia ............................................................................................................................................... 3

6 Apparatus .............................................................................................................................................. 3

6.1 General ................................................................................................................................................... 3

6.2 Automatic titration equipment ...................................................................................................... 3

6.3 Indicator electrode ............................................................................................................................ 3

6.4 Reference electrode ........................................................................................................................... 3

6.5 Pipette .................................................................................................................................................... 3

7 Sampling and sample pretreatment ............................................................................................. 4

7.1 General ................................................................................................................................................... 4

7.2 White, green and black liquors ...................................................................................................... 4

7.3 Oxidized white liquors ...................................................................................................................... 4

8 Procedure ............................................................................................................................................. 4

8.1 White, green and black liquors ...................................................................................................... 4

8.2 Oxidized white liquors ...................................................................................................................... 5

8.3 Titration ................................................................................................................................................ 5

9 Calculation ............................................................................................................................................ 6

10 Report .................................................................................................................................................... 7

Annex A (informative) Precision data ....................................................................................................... 8

Bibliography ...................................................................................................................................................... 9

Formatted: Font: 11 pt
Formatted: Space After: 6 pt, Line spacing: Exactly 11
© ISO 2022 – All rights reserved 5
© ISO 2022 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO/FDIS 23777:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO

collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directiveswww.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any

patent rights identified during the development of the document will be in the Introduction and/or on

the ISO list of patent declarations received (see www.iso.org/patentswww.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at
www.iso.org/members.htmlwww.iso.org/members.html.
Formatted: Font: 11 pt
Formatted: Space After: 6 pt, Line spacing: Exactly 11
6 © ISO 2022 – All rights reserved
vi © ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23777:2022(E)
Pulps — Kraft liquor — Determination of hydrosulphide ion
concentration using potentiometric titration
1 Scope

This document describes a procedure for the determination of sulphide, i.e. the hydrosulphide ion

concentration, in white, oxidized white and green liquors, as well as in black liquor having a dry matter

content up to 40 %. The determination also includes the sulphide part of any polysulphide present in the

solution.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/

3.1
hydrosulphide ion concentration
concentration in white, black and green liquors or oxidized white liquor

Note 1 to entry: Practically no S ions are present in white, oxidized white, green, and black liquors because of

hydrolysis according to the reaction:
2− −−
S + H O→+HS OH
2− − −
Field Code Changed
S + H O→+HS OH
4 Principle

The procedure is based on potentiometric titration with silver nitrate solution according to

reaction (1) and (2):
− − + − − +
Field Code Changed
HS ++OH 2Ag → Ag S + H O HS ++OH 2Ag → Ag S + H O (1)
22black ppt 22black ppt
( ) ( )
− + − +
Field Code Changed
CH S +→Ag AgCH S CH S +→Ag AgCH S (2)
3 3 ( yellow ppt) 3 3 ( yellow ppt)
© ISO 2022 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO/FDIS 23777:2022(E)
Formatted: Font: 12 pt

Sulphite ions are added to the sample solution in order to dissolve any polysulphide ions that are present

according to reaction (3):
2− 2− 2−− − 2− 2− 2− − −
Field Code Changed
nSO + S S + H O→ nS O + HS + OH nSO + S S + H O→ nS O + HS + OH (3)
3 n 2 23 3 n 2 2 3

Each polysulphide ion thus contributes one sulphide ion to the sulphide content. As the titration is

performed in alkaline solution, thiosulphate or sulphite ions do not interfere in the determination.

When sulphite ions are added to organic polysulphides, mercaptide ions are produced according to

reacionreaction (4):
2− −−
Field Code Changed
CH SSCH +→SO CH SSO + CH S
2− −−
3 3 3 3 3 3
CH SSCH +→SO CH SSO + CH S (4)
3 3 3 3 3 3
For white, green and black liquor, this document i
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23777
ISO/TC 6
Pulps — Kraft liquor — Determination
Secretariat: SCC
of hydrosulphide ion concentration
Voting begins on:
2022-12-09 using potentiometric titration
Voting terminates on:
2023-02-03
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 23777:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2022
---------------------- Page: 1 ----------------------
ISO/FDIS 23777:2022(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23777
ISO/TC 6
Pulps — Kraft liquor — Determination
Secretariat: SCC
of hydrosulphide ion concentration
Voting begins on:
using potentiometric titration
Voting terminates on:
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: +41 22 749 01 11
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 23777:2022(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
© ISO 2022 – All rights reserved
NATIONAL REGULATIONS. © ISO 2022
---------------------- Page: 2 ----------------------
ISO/FDIS 23777:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Reagents ........................................................................................................................................................................................................................ 2

6 Apparatus .................................................................................................................................................................................................................... 3

7 Sampling and sample pretreatment................................................................................................................................................3

7.1 General ........................................................................................................................................................................................................... 3

7.2 White, green and black liquors ................................................................................................................................................ 3

7.3 Oxidized white liquors..................................................................................................................................................................... 3

8 Procedure ....................................................................................................................................................................................................................4

8.1 General ........................................................................................................................................................................................................... 4

8.2 White, green and black liquors ................................................................................................................................................ 4

8.3 Oxidized white liquors..................................................................................................................................................................... 4

8.4 Titration........................................................................................................................................................................................................ 4

9 Calculation .................................................................................................................................................................................................................. 5

10 Report .............................................................................................................................................................................................................................. 6

Annex A (informative) Precision data ................................................................................................................................................................ 7

Bibliography ................................................................................................................................................................................................................................ 8

iii
© ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/FDIS 23777:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23777:2022(E)
Pulps — Kraft liquor — Determination of hydrosulphide
ion concentration using potentiometric titration
1 Scope

This document describes a procedure for the determination of sulphide, i.e. the hydrosulphide ion

concentration, in white, oxidized white and green liquors, as well as in black liquor having a dry matter

content up to 40 %. The determination also includes the sulphide part of any polysulphide present in

the solution.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
hydrosulphide ion concentration
concentration in white, black and green liquors or oxidized white liquor

Note 1 to entry: Practically no S ions are present in white, oxidized white, green, and black liquors because of

hydrolysis according to the reaction:
2−− −
SH+→OHSO+ H
4 Principle

The procedure is based on potentiometric titration with silver nitrate solution according to

reaction (1) and (2):
−− +
HS ++OH 2Ag →+Ag SH O (1)
22()black ppt
CH SA+→gAgCHS (2)
33 ()yellowppt

Sulphite ions are added to the sample solution in order to dissolve any polysulphide ions that are

present according to reaction (3):
2−−2−−2 −
nSOS++SH On→+SO HS +OH (3)
3 n 22 3

Each polysulphide ion thus contributes one sulphide ion to the sulphide content. As the titration is

performed in alkaline solution, thiosulphate or sulphite ions do not interfere in the determination.

© ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
ISO/FDIS 23777:2022(E)

When sulphite ions are added to organic polysulphides, mercaptide ions are produced according to

reaction (4):
2−− −
CH SSCHS+→OCH SSO +CH S (4)
33 3 33 3

For white, green and black liquor, this document is applicable for hydrosulphide ion concentrations

from 0,02 mol/litre to 2 mol/litre, provided that the volume of the original sample taken to analysis

is selected accordingly. For oxidized white liquors the standard is applicable to hydrosulphide ion

concentrations from 0,5 mmol/litre to 50 mmol/litre, provided that the volume of the original sample

taken to analysis is selected accordingly.
Precision data are available in Annex A.
5 Reagents
All chemicals shall be of analytical grade.
5.1 Water, use oxygen-free water for the preparation of the solutions.

NOTE Oxygen-free water can be prepared from distilled water either by boiling the water for 15 min or by

displacing the oxygen with nitrogen gas.

5.2 Silver nitrate 0,1 M, dissolve 17,0 g of dry silver nitrate, AgNO , in a 1 000 ml volumetric flask.

Stir and fill up to the mark with water (5.1). Determine the concentration in the following way:

Weigh approximately 750 mg of dried potassium chloride, KCl, to an accuracy of 0,5 mg into a 100 ml

volumetric flask and fill up to the mark with water (5.1). With a precision pipette, take 5 ml for titration

in distilled water. Titrate with the silver nitrate solution to the first inflection point. From the silver

nitrate consumption, a ml, calculate the silver nitrate concentration in moles/litre to fo

...

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